This invention concerns lights for illuminating potential leak sites in air conditioning and refrigeration equipment, for both building and automotive applications, as well as for detecting fluid leaks in other sealed systems such automotive radiators, transmissions, crankcases, etc. It has been known to use fluorescing dyes, typically mixed with lubricants, and injected into the sealed equipment. If any of the dye leaks out at potential leak sites, the dye will fluoresce when illuminated and thus be easily detected by a technician who can thereby find any leaks that exist.
These dyes will fluoresce when illuminated with light and the light emitted from such dyes is in the visible range. Typical dyes used for this purpose fluoresce in this manner when illuminated with ultraviolet light and also in visible blue wavelengths.
For this reason, light sources have been developed which are intended to generate ultraviolet light of wavelengths ranging from about 300 nm to over 400 nm in the near UV or visible blue range. See U.S. Pat. No. 5,905,268 for an example of such a light, in which dichroic filters are used to prevent transmission of visible light other than blue light used to excite the dye. These filters rely on an interference reflection phenomenon as described in that patent.
The visibility of the resulting light emission to an observer is somewhat lessened by the presence of the visible blue light in the light beam emanating from the source, as this light reflects from the surfaces and reduces the contrast of any light emitted from the fluorescent dye.
This has led to the need to use xe2x80x9cblue blockerxe2x80x9d eyeglasses, which block out the blue light reflected from the surfaces around the potential leak sites when illuminating the same with the examining light. See copending U.S. application Ser. No. 08/964,834, filed on Nov. 5, 1997, and U.S. Pat. No. 5,674,000, issued Oct. 2, 1997.
When xe2x80x9cdeepxe2x80x9d UV radiation is present, i.e., substantially under 340 nm wavelengths, a potential safety hazard is created in that such short wavelengths could be reflected so as to harm the eyes of the technician performing the inspection.
This safety hazard is also avoided by the xe2x80x9cblue blockingxe2x80x9d eyewear which is also designed to block UV radiation.
The requirement to use eyewear when conducting inspections is a disadvantage as it requires an extra item of equipment, and entails the inconvenience of finding and putting on the eyewear when conducting inspections.
It is the object of the invention to provide a light source and method for carrying out such leak detection inspections which eliminates the need for using blocking eyewear to increase the contrast of the fluorescent light emissions or to protect the eyes from deep UV radiation.
Another poorly understood problem with the use of dichroic blue filters of the type cited in U.S. Pat. No. 5,905,268 is that in fact there is poor transmission of UV by most of these filters. The Balzar AGB46 Dicholight filter described in the patent as having a transmission characteristic peaking on the UV range in fact does not transmit UV appreciably. It is believed that the reason for this poor UV transmission is the selection of coating material, such as titanium oxide.
While the interferences set up by the coating thicknesses can be calculated to pass or absorb any given range of wavelengths, the coating material itself will characteristically absorb particular wavelengths.
The end result is to preclude use of a pure xe2x80x9cblackxe2x80x9d light, created by such a dichroic filter, as little dye exciting light will be produced by the light.
Accordingly, another object of the present invention is to provide a light source for the leak detection field which generates a light beam of substantially pure UV light by using a dichroic filter having a UV transmitting characteristic which enables a beam of powerful intensity when compared to other lights using dichroic filters commonly used for this application.
The present invention contemplates mounting a dichroic or reflecting type filter which is coated with a number of alternating layers, preferably alternately with tantalum pentoxide and silicon dioxide or with hafnium dioxide and silicone dioxide of a thickness suitable to cause interference reflection of xe2x80x9cdeepxe2x80x9d UV light, i.e., shorter than 340 nm, and also of visible light, (over 380 nm up to 720 nm). Such coatings are preferably applied by ion assisted deposition.
Techniques producing reflection of these wavelengths by interference are well known to those skilled in the art.
A UV anti-reflection coating of magnesium fluoride on the outer surface of the filter further improves UV transmission.
Wavelengths over 720 nm are transmitted to eliminate infrared heating of the filter or other components.
A high power light source which emits UV radiation is used in conjunction with the dichroic filter.